Bile acid diarrhea (BAD) is a cause of chronic, watery diarrhea often incorrectly diagnosed as irritable bowel syndrome with diarrhea (IBS-D). Recognizing BAD is important because it requires a specific, targeted treatment that differs significantly from standard chronic diarrhea management. Effective relief from the frequent and urgent bowel movements associated with this disorder begins with accurate diagnosis and a tailored approach to medication and diet.
Why Bile Acids Cause Diarrhea
Bile acids are compounds produced by the liver and stored in the gallbladder, playing a crucial role in the digestion and absorption of fats in the small intestine. The body is highly efficient at recycling them, with approximately 95% of bile acids being reabsorbed in the terminal ileum. This reabsorbed bile is returned to the liver to be reused in a process known as the enterohepatic circulation.
Bile acid diarrhea occurs when this recycling process fails, causing an excessive amount of bile acids to spill into the colon. Once in the colon, these unabsorbed bile acids act as irritants and laxatives. They stimulate the colon lining to secrete water and electrolytes, which significantly increases the fluid content of the stool.
The presence of bile acids in the colon also speeds up the muscular contractions, or motility, of the large intestine. This combination of increased fluid secretion and accelerated transit time results in the characteristic symptom of chronic, watery diarrhea. The excess bile acids are also responsible for the urgency and abdominal discomfort experienced by many individuals.
Bile acid diarrhea is categorized into three main types based on the underlying cause. Type 1 is secondary to diseases or surgeries that directly damage the terminal ileum, such as Crohn’s disease or surgical resection. Type 3 is secondary to various other gastrointestinal issues like celiac disease or gallbladder removal (cholecystectomy).
Type 2, or primary BAD, is the most common form and occurs without any detectable underlying intestinal disease. In this idiopathic type, the liver produces too many bile acids for the ileum to reabsorb, often due to a disruption in the hormonal feedback loop that regulates bile acid synthesis.
How Doctors Diagnose Bile Acid Diarrhea
Confirming a diagnosis of bile acid diarrhea is necessary to initiate the specific treatment that provides relief. The most definitive test, considered the gold standard in many countries, is the \({}^{75}\text{SeHCAT}\) scan, which measures the body’s ability to retain a synthetic bile acid over a period of time. This test involves swallowing a capsule containing a small amount of a radioactive tracer bound to a synthetic bile acid.
The patient attends two appointments seven days apart, where a specialized camera measures the amount of tracer remaining in the body. If less than 15% of the tracer is retained in the body after seven days, it confirms a diagnosis of bile acid diarrhea. A lower retention percentage correlates with a greater loss of bile acids and more severe disease.
Since the \({}^{75}\text{SeHCAT}\) scan is not universally available, doctors often rely on less invasive blood and stool tests. One such method is measuring the level of 7-alpha-hydroxy-4-cholesten-3-one (C4) in the blood. C4 is a precursor molecule in the liver’s process of making new bile acids, and high levels indicate the liver is overcompensating for bile acid loss.
Another common approach is a diagnostic therapeutic trial, where a patient with suspected BAD is simply given a targeted medication. If the diarrhea symptoms improve significantly, it is considered highly suggestive of bile acid diarrhea, even without formal testing.
Medication Options for Management
The primary pharmacological treatment for bile acid diarrhea involves a class of prescription medications known as bile acid sequestrants (BAS). These drugs are designed to directly address the problem by binding to the excess bile acids in the intestinal tract. They form a complex that prevents the bile acids from irritating the colon and forces them to be safely eliminated in the stool.
Cholestyramine (Questran) is one of the most widely used sequestrants, typically started at a low dose of 2 to 4 grams per day and gradually increased based on the patient’s response. The maximum effective dose can range up to 16 grams daily. However, this medication is a powder that must be mixed with liquid, and its gritty texture and taste can sometimes make it difficult for patients to tolerate.
Colestipol (Colestid) is another option, available in both powder and tablet form, which can be started at a dose of 1 to 2 grams taken once or twice daily. The dose is incrementally increased until symptoms are controlled, with a maximum dose of up to 16 grams per day for tablets. Like Cholestyramine, it can cause gastrointestinal side effects, such as bloating and constipation, which often requires careful dose titration.
Colesevelam (Welchol) is a newer generation sequestrant that is only available as a tablet and is generally better tolerated than the older powders. The typical dose is between 2 to 6 tablets daily. Because BAS medications bind to other substances in the gut, they can interfere with the absorption of other medications. Patients are usually advised to take all other medications one hour before or four to six hours after taking the sequestrant.
Dietary and Lifestyle Changes to Help Management
Non-pharmacological strategies complement medication by reducing the overall demand for bile acids and managing the effects of chronic diarrhea. Since bile acids are released to process fats, reducing dietary fat intake automatically lowers the amount of bile acids needed for digestion. A low-fat diet, aiming for a total fat intake of around 40 grams per day, can significantly lessen symptoms.
It is helpful to spread fat consumption evenly throughout the day, avoiding large amounts of fat in a single meal, as this triggers a massive release of bile acids. Patients should focus on lean proteins, low-fat dairy, and healthy, monounsaturated fats in moderation, while strictly limiting fried foods, creamy sauces, and high-fat baked goods.
Increasing the intake of soluble fiber is also beneficial, as it dissolves in water to form a gel-like substance in the gut. This gel helps to slow intestinal transit time and bulk up the stool, making it firmer and less watery. Good sources of soluble fiber include oats, barley, applesauce, and psyllium-based supplements.
Chronic diarrhea causes a substantial loss of both water and electrolytes, putting individuals at risk of dehydration. Maintaining adequate hydration is necessary. Electrolytes, such as sodium and potassium, must be replaced using oral rehydration solutions, sports drinks, or salty broths to prevent fatigue, muscle cramps, and other complications associated with mineral imbalance.